list_instances

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden of behavioral disclosure. It explicitly discloses the read-only safety property ('Read-only, so it is safe to point at instances someone else owns'), which is the key behavioral trait an agent needs. It does not contradict any annotations since none exist.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, front-loaded with the core purpose ('What is running'), followed by reported fields, then safety and use case. Zero wasted words; every sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description usefully enumerates the returned fields and that coverage is complete for a read-only enumeration tool. The only mild gap is that the output format/ordering is unspecified, which is a minor omission for a listing tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline 3 applies even without param detail in the description. The description adds conceptual framing (the port sweep relation to 'games that predate the registry') but the schema already documents scan, prune, range, and registry thoroughly, including the dangerous prune default behavior.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Leads with a specific verb and object — 'What is running: instances that self-registered, plus a sweep of the configured port range'. It names the exact fields reported (name, version, pid, working directory, current screen) and the two discovery sources (registry vs scan), and the read-only framing plus the 'attach to a game you did not launch' use case clearly separates it from the launch/stop/log siblings.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit purpose statement — 'Use it to attach to a game you did not launch' — and explains the two data sources, which signals when a scan is needed (old instances) vs the registry alone. It does not explicitly name when NOT to use it or point to an alternative (e.g. instance_log for logs), but the context is clear enough for an agent to select it for enumeration.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.